ch. 33 slides
TRANSCRIPT
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Phys 133 -- Chapter 33 1
Chapter 33
Electromagnetic Induction
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Phys 133 -- Chapter 33 2
Demo Faraday
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Phys 133 -- Chapter 33 3
Some experiments
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Phys 133 -- Chapter 33 4
Motional emf
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Phys 133 -- Chapter 33 5
Motional emf (cont.)Reach equilibrium
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Phys 133 -- Chapter 33 6
A potential difference of 0.050 V is developed across a 10-cm long wire as it moves through a magnetic field at 5.0 m/s. The magnetic field is perpendicular to the wire axis. What are strength and direction of field?
Problem 33.1
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Phys 133 -- Chapter 33 7
Problem 33.1 (ans)At equilibrium
FeFm
Out of page
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Phys 133 -- Chapter 33 8
--moving charges in B field, force --> current
--current-carrying wire in field, force
Induced current
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Phys 133 -- Chapter 33 9
Do workbook 33.1
Answer:A)ClockwiseB)Counter-clockwiseC)No current
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Phys 133 -- Chapter 33 10
Eddy currents
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Phys 133 -- Chapter 33 11
Do workbook 33.2 & 4
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Phys 133 -- Chapter 33 12
Eddy currents (cont.)
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Phys 133 -- Chapter 33 13
Demo eddy currents
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Phys 133 -- Chapter 33 14
Do workbook 33.4
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Phys 133 -- Chapter 33 15
Magnetic flux
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Phys 133 -- Chapter 33 16
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Phys 133 -- Chapter 33 17
There is an induced current in a closed, conducting loop if and only if the magnetic flux through the loop is changing. The induced current creates an induced magnetic field which opposes the change in flux.
--changing flux produces induced current
--induced current creates induced field
--induced field opposes the change
Lenz’s law
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Phys 133 -- Chapter 33 18
Does the loop of wire have a clockwise current, a counterclockwise current, or no current under the following circumstances?A)CWB)CCWC)No current
1)The magnetic field strength is increasing?2)The magnetic field strength is constant?3)The magnetic field strength is decreasing?
Two loops of wire are stacked vertically, one above the other. Does the upper loop have current in the following circumstances.A)CWB)CCWC)No current?
1)Before the switch is closed?2)Immediately after the switch is closed?3)Long after the switch is closed?4)Immediately after the switch is reopened?
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Phys 133 -- Chapter 33 19
1) As the magnet is inserted into the coil, does current flow right to left or left to right through the current meter, or is the current zero?
2) As the magnet is held at rest inside the coil…?
3) As the magnet is withdrawn from the coil…?
4) If the magnet is inserted into the coil more rapidly than in part a, does the size of the current increase, decrease or stay the same? Explain
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Phys 133 -- Chapter 33 20
Do workbook 33.12, 13 & 19
c. Just after the switch on the left coil is reopened, does current flow right to left or left to right through the current meter of the right coil? Or is the current zero?
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Phys 133 -- Chapter 33 21
The current in the solenoid is decreasing. The solenoid is surrounded by a conducting loop. Is there a current in the loop? If so, is the current in the loop cw or ccw?
Problem 33.9
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Phys 133 -- Chapter 33 22
Problem 33.9 (ans)
B1
Initially
later
B2
∆Change in flux to left
• Find change in flux
• Find induced field
Induced field points to right
• Find induced currentInduced current is clockwise from behind
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Phys 133 -- Chapter 33 23
field is there independent of wireInduced fields
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Phys 133 -- Chapter 33 24
--law of nature
--usually helpful
Faraday’s law
-field can change
-area can change
-both can change
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Phys 133 -- Chapter 33 25
Do workbook 33.21
A conducting loop around a magnetic field contains two bulbs, A and B. The wires connecting the bulbs are ideal, with no resistance. The magnetic field is increasing rapidly.
1) Do the bulbs glow? Why or why not?
2) If they glow, which bulb is brighter? Or are they equally bright? Explain.
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Phys 133 -- Chapter 33 26
Problem 33.12bThe loop is being pushed out of the 0.20 T magnetic field at 50 m/s. The resistance of the loop is 0.20 . What are the direction and magnitude of current in the loop?
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Phys 133 -- Chapter 33 27
Problem 33.12b (ans)
L
w
Counter-clockwise
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Phys 133 -- Chapter 33 28
Two 20-turn coils are tightly wrapped on the same 2.0-cm-diameter cylinder with 1.0-mm-diameter wire. The current through coil 1 is shown. A positive current is into the page at the top of the loop. Determine the current in coil 2 as current vs. time t = 0 s to 0.4 s. (Assume field of coil 1 passes completely through coil 2.
0.1 0.3
Problem 33.35
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Phys 133 -- Chapter 33 29
Problem 33.35 (ans)
B1
(+)
2
I1
d2/dt
2
I2
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Phys 133 -- Chapter 33 30
Problem 33.35 (ans)
(+)
I1
I2
Right to left through resistor
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Phys 133 -- Chapter 33 31
Generator
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Phys 133 -- Chapter 33 32
Transformer
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Phys 133 -- Chapter 33 33
Coulomb and non-Coulomb electric fields
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Phys 133 -- Chapter 33 34
-symmetric in E and B
Maxwell and induced magnetic field
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Phys 133 -- Chapter 33 35
E & M equations
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Phys 133 -- Chapter 33 36
Maxwell’s equations
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Phys 133 -- Chapter 33 37
+math
Light is an E&M wave!!!
Maxwell-no charges or current
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Phys 133 -- Chapter 33 38
EM waves
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Phys 133 -- Chapter 33 39
Problem 33.49A U-shaped conducting rail that is oriented
vertically in a horizontal magnetic field. The rail has no electrical resistance and does not move. A slide wire with mass m and resistance R can slide up and down without friction while maintaining electrical contact with the rail. The slide wire is release from rest.
a) Describe the motion of the slide wire.b) Find the terminal velocity of the slide wire